The present invention relates generally to electrolytic gas generators and relates more particularly to a novel electrolytic gas generator and to an implant system comprising the same.
The controlled generation of one or more types of gases at point-of-use is of significance to a multitude of industrial and medical applications. Electrolysis is a common technique for generating such gases and typically involves converting a feedstock (which is often a low cost, stable reactant) to a useful commodity (which is often a high cost or unstable product) using an electrical current. Electrolysis is favored as a production technique due to its high process efficiency, its product selectivity, and its inherent ability to control production rate by controlling the applied current. Devices designed to generate one or more gases using electrolysis are sometimes referred to as electrolytic gas generators. Electrolytic gas generators for hydrogen production, for instance, are used frequently in analytical laboratories to supply high purity hydrogen, on-demand, for use as carrier and detector gases in gas chromatographs. Electrolytic gas generators for oxygen production, for example, have been used to generate oxygen in situ at skin wounds to improve the healing process for severe burns and diabetic ulcers. Such electrolytic gas generators typically require several basic system components to govern performance and safety, and these basic system components generally include current control (e.g., a DC power supply for maintaining generation rate and voltage efficiency), downstream pressure and gas purity monitoring (e.g., for process and environmental safety), and fluid management (e.g., water reactant feed pump and gas-liquid separation units). However, as can be appreciated, such components can increase the size, cost, and complexity of the overall system and can make the overall system more difficult to maintain. Also, although hydrogen and oxygen are two of the more common gases produced by electrolytic gas generators, electrolytic gas generators can be used to produce other gases, such as, but not limited to, carbon dioxide, chlorine, ozone, hydrogen peroxide, chlorine dioxide, nitric oxide, sulfur dioxide, hydrogen sulfide, carbon monoxide, ammonia, hydrogen chloride, hydrogen bromide, and hydrogen cyanide.
An emerging medical application for in situ gas generation is in the provision of gaseous oxygen to cells and/or tissues that are located under the skin or that are included as part of a subdermal implant device. Subdermal implant devices are useful implements for the in situ generation and dissemination of therapeutics to a patient in need thereof for the treatment of various diseases, disorders, and/or conditions. Typically, such implant devices comprise cells and/or tissues that are encapsulated within a suitable implantable container. The implantable container is typically designed to allow the cells and/or tissues to produce the desired therapeutic and for the dissemination of the produced therapeutic to the patient while, at the same time, limiting an immunological response. As can be appreciated, the delivery of essential gases (e.g., oxygen) and nutrients to implant devices is important for the viability and function of the cells and/or tissues contained therein. Regarding the delivery of gases to the implant device, it is especially important to the safety of the patient that excessive gas pressures be prevented and/or mitigated so as to obviate the risk of pain, infection, tissue damage, or embolism in the patient.
In U.S. Patent Application Publication No. US 2015/0112247 A1, inventors Tempelman et al., which was published Apr. 23, 2015, and which is incorporated herein by reference in its entirety, there is disclosed a system for gas treatment of a cell implant. According to the aforementioned publication (hereinafter “the '247 publication”), the system enhances the viability and function of cellular implants, particularly those with high cellular density, for use in human or veterinary medicine. The system utilizes a miniaturized electrochemical gas generator subsystem that continuously supplies oxygen and/or hydrogen to cells within an implantable and immunoisolated cell containment subsystem to facilitate cell viability and function at high cellular density while minimizing overall implant size. The cell containment subsystem is equipped with features to allow gas delivery through porous tubing or gas-only permeable internal gas compartments within the implantable cell containment subsystem. Furthermore, the gas generator subsystem includes components that allow access to water for electrolysis while implanted, thereby promoting long-term implantability of the gas generator subsystem. An application of the system is a pancreatic islet (or pancreatic islet analogue) implant for treatment of Type I diabetes (T1D) that would be considered a bio-artificial pancreas.
In U.S. Pat. No. 7,892,222 B2, inventors Vardi et al., which issued Feb. 22, 2011, and which is incorporated herein by reference in its entirety, there is disclosed an implantable device comprising a chamber for holding functional cells and an oxygen generator for providing oxygen to the cells within the chamber. According to the aforementioned patent (hereinafter “the '222 patent”), functional cells are loaded into the chamber of the device that is then implanted in the body. The device comprises an oxygen generator, i.e., an element that can produce oxygen and make it available to the functional cells, so that the functional cells do not suffer from hypoxia. The oxygen generator thus produces oxygen and typically releases the oxygen in the cell's vicinity. In one embodiment, the oxygen generator comprises a pair of electrodes. When an electric potential is applied across the electrodes, oxygen is released by electrolysis of ambient water molecules present within the chamber. The electrodes are connected to a power source, typically a rechargeable battery. The chamber may further comprise an oxygen sensor that determines the oxygen concentration in the vicinity of the functional cells. A microprocessor may be provided to turn on the oxygen generator when the sensor detects that the oxygen concentration is below a predetermined minimum and to turn it off when the oxygen concentration is above a predetermined maximum.
In U.S. Pat. No. 6,368,592 B1, inventors Colton et al., which issued Apr. 9, 2002, and which is incorporated herein by reference in its entirety, there is disclosed a method of delivering oxygen to cells by electrolyzing water. According to the aforementioned patent (hereinafter “the '592 patent”), oxygen is supplied to cells in vitro or in vivo by generating oxygen with an oxygen generator that electrolyzes water to oxygen and hydrogen. Oxygen can be generated substantially without generating free hydrogen using a multilayer electrolyzer sheet having a proton exchange membrane sandwiched by an anode layer and a cathode layer. The oxygen generator may be used to supply oxygen to cells contained by a culture plate, a culture flask, a microtiter plate or an extracorporeal circuit, or to cells in an encapsulating chamber for implanting in the body such as an immunoisolation chamber bounded by a semipermeable barrier layer that allows selected components to enter and leave the chamber. A bioactive molecule may be present with the cells. Oxygen can be delivered in situ to cells within the body such as by implanting the oxygen generator in proximity to cell-containing microcapsules in an intraperitoneal space, or by implanting a system containing the oxygen generator in proximity to an immunoisolation chamber containing cells. The oxygen generator may be connected to a current control circuit and a power supply.
One shortcoming that has been identified by the present inventors with electrolytic gas generators of the type conventionally used with subdermal implant devices is that such electrolytic gas generators either are configured to continuously generate a gas (which, in most cases, is oxygen) or are equipped with some external mechanism, such as a gas sensor and a current control device, to control actuation of the electrolytic gas generator. However, the continuous generation of gas may be undesirable for a subdermal implant device, especially if the rate of gas generation exceeds the rate at which the generated gas is consumed by cells and/or tissues of the implant device, as excess gas can lead to damage to the implant and/or the patient. On the other hand, external mechanisms for controlling gas generation can increase the size of the implant, which is undesirable, as well as adding to the cost and complexity of the implant.